Find free stock photos with Veezzle. Use this search engine to find photos from Flickr, Wikimedia Commons and other sites. Click on the photo you want and it will take you there. You may need to sign up for some of the photos (the rbgstock photos require registration to download, for example), and the photos on the left side of the page are not free. But this is one more place to search for Creative Commons images you can use for your posters and projects. Remember, you still need to attribute and hyperlink.
I found this photo by searching “hydrangea”: